A murder investigation is under way after a British sailor was found seriously injured on board a burning life raft in the Caribbean.

A diving instructor found John Garner with head and leg injuries and surrounded by debris, oil and thick smoke off the coast of St Vincent.

He was pronounced dead on arrival at hospital yesterday afternoon.

Police have now launched a murder inquiry and are understood to be searching for a woman named Heidi Hukkelaas, believed to be Mr Garner's Norwegian wife.

St Vincent police commissioner Michael Charles confirmed they are treating the death as suspicious and they are looking at "all lines of inquiry".

He said: "We suspect foul play and will investigate the matter fully. Miss Hukkelaas is a person of interest and, as with every murder investigation, we have to look at everyone and everything and will leave no stones unturned."

Kay Wilson, who was first on the scene, said she found Mr Garner with "bad injuries" including cuts to his face and legs.

It became "pretty evident that we were not going to be able to help him", said Ms Wilson, who was captaining a passenger diving trip.

The witness said she believed it may have been "an accident, an explosion of some kind".

She said there was so much black smoke that by the time they reached the stricken boat it had already been engulfed by flames.

She said: "It was almost razed to the water line, and the heat and the smoke which were coming were just incredible."

The vessel was "almost underwater" and it looked like Mr Garner had tried to deploy his life raft but it did not deploy properly, she said.

Ms Wilson added: "Behind the boat there was debris in every direction and the wind was carrying the debris from the boat. I think it was an indication there had been an explosion on board because there was so much stuff in the water - garbage from the galley and small pieces of debris.

"We found him (Mr Garner) very close relatively to his yacht, probably about 150-200ft downwind, floating in the water.

"He was wearing a lifejacket that inflates when you hit the water. It had inflated and was holding him up."

Of the suspicions surrounding the death, Ms Wilson said: "My initial impression was that it was an accident. There is the fact that it had happened around lunchtime and there was an explosion on board. The injuries this person had was, from my perspective, that something had exploded in his face and he had injuries to his face and leg.

"I did not see any defensive wounds or anything that would suggest that there was foul play."

Ms Wilson also said she had been contacted by Mr Garner's son, adding that Mr Garner had been spending time on the Grenadines island of Bequia with another family member, dropping them back to return to their home before planning to make his way to Antigua.

The yacht is reportedly named Asante and registered in Gibraltar.

The Jamaica Observer said a preliminary police investigation found that Mr Garner and Ms Hukkelaas had arrived in St Vincent and the Grenadines by air on January 19, and they had been granted an extension to remain until April 19.

The newspaper said checks had revealed that Ms Hukkelaas had not left the state by any of its air or sea ports.

A Foreign Office spokesman said: "We are aware of the death of a British national in St Vincent and the Grenadines. We are providing consular assistance to the family at this difficult time."